Computer Network after midterm Lecture by B@NK

Network layer

Network Layer

o transport segment from o

Part I

o

Computer Networks

o o

application transport network data link physical p y

sending to receiving host on sending d side d encapsulates segments into datagrams g m on receiving side, delivers segments to t transport t layer l network layer protocols in every host, router Router examines header fields in all IP datagrams passing i th through h it

network data link physical

o forwarding: move packets from router router’ss analogy: input link interface to o routing: process of appropriate pp p router planning l i trip t i from f output link interface source to destination o routing: determine o forwarding: process route (end-to-end of getting through path) taken by single i l interchange i h packets from source to destination o Routing Algorithms

Network Layer

network data link physical

network data link physical network data link physical

network network data link data link physical physical network data link physical

network data link physical

Network Layer

Two K Key y Network-Layer L y Functions F

network data link physical

network data link physical

network data link physical

application transport network data link physical

Network Layer

Interplay between routing and forwarding routing algorithm

local forwarding table header value output link 0100 0101 0111 1001

3 2 2 1

value in arriving packet’s header 0111

1 3 2

Network Layer

Connection setup

Network Service Models

o 3rd important function in some network architectures: o Asynchronous Transfer Mode (ATM), Frame Relay, X.25 o Backbone B kb networks t k in i Internet I t t are Switched S it h d WAN o Switched WAN : wide area network that cover large area and provide access at several point to users o before datagrams flow, two end hosts and intervening routers establish virtual connection o routers get involved

o defining characteristics of end-to-end

transport of packets between sending and receiving end systems o Some possible services for individual datagrams (packets) : o o

DTE : Data Terminating Equipment DCE : Data Circuit Equipment

UNI : User-to-Network Interface NNI : Network-to-Network Interface

Guaranteed delivery : packet will eventually arrive at destination Guaranteed delivery with bounded delay : not only guarantees t d delivery li of f pkt, kt b butt d delivery li within ithi specified host-to-host delay bound (ex. within 100 msec.))

Network Layer

Network Service Models (cont.s) ( )

Network Layer

Network layer y service models: m

o Some possible services for flow of

datagrams g (packets) (p ): o

In-order packet delivery : o packets arrive at destination in the order that they were sent

o

Guaranteed minimal bandwidth : o Emulating g behavior of transmission link of a specified p bit rate between sending and receiving hosts o As long as sending host transmits bits at a rate below specified p bit rate, then no p packet is lost and each packet arrives with in a prespecified host-to-host delay

o

Guaranteed maximum jitter o Amount of time between transmission of two successive pkts at sender is equal to amount of time between their receipt at destination Network Layer

Network Architecture Internet

Service Model

Guarantees ?

Congestion Bandwidth Loss Order Timing feedback

best effort none

no

no

no

yes

yes

yes

yes

no

ATM

CBR

constant Rate

ATM

ABR

guaranteed no minimum

no (inferred via loss) no Congestion g will Not occur Yes (congestion indication provided)

Network Layer

Network layer connection and connection-less ti l ss service s i

Virtual Circuits (VC) “source-to-destination path behaves much like telephone circuit”

o Network layer y Connection service o Virtual Circuit

o Connection setup o Forwarding o Routing

o o

o Network layer y Connection-less service o Datagram network o Forwarding o Routing

o Analogous to the transport-layer services, but: o service: host-to-host o no choice: h i network k provides id one or the h other h o implementation: in network core

Network Layer

VC implementation

performance-wise network actions along source source-to-destination to destination path

o call setup, teardown for each call before data can flow o each packet carries VC identifier (VCI) (not destination host address) o every router on source-destination path maintains “state” for each passing connection o link, router resources (bandwidth, buffers) may be allocated to VC (dedicated resources = predictable service) Network Layer

Forwarding table

VC number 22

12

1

o

a VC consists of: o Path from source to destination (Virtual Path: VP) o VC numbers, one number for each link along path o entries in forwarding tables in routers along path o packet belonging to VC carries VC number (rather than destination address) o VC number can be changed on each link. o New VC number comes from forwarding table Note that a virtual connection is defined by a pair of Network Layer numbers: VPI and VCI.

Forwarding table in n th st router: northwest t : Incoming interface 1 2 3 1 …

2

32

3

interface number

Incoming VC # 12 63 7 97 …

Outgoing interface 3 1 2 3 …

Outgoing VC # 22 18 17 87 …

R Routers maintain i i connection i state information! i f i !

Network Layer

Virtual circuits: signaling g g protocols p o used to setup, maintain teardown VC o used in ATM, Frame-Relay, X.25

o no call setup at network layer o routers: no state about end-to-end connections o no network-level concept of “connection”

o packets forwarded using destination host address

o not used in today’s Internet

application l transport 5. Data flow begins network 4. Call connected 1 Initiate call data link 1. physical

Datagram networks

o packets between same source-dest pair may take different paths 6. Receive data application 3. Accept call transport 2 incoming call network 2.

data link physical

application transport network data link 1. Send data physical

application transport p 2. Receive data network data link physical

Network Layer

Forwarding Forward ng table

4 billion possible entries

Network Layer

Longest prefix pref x matching match ng

Examples DA: 11001000 00010111 00010110 10100001

Which interface?

DA: 11001000 00010111 00011000 10101010

Which interface?

Router users the longest prefix matching rule Network Layer

Network Layer

What is inside the router? : Router Architecture Overview

Input nput Port ort Funct Functions ons

o Two key router functions: o run routing g algorithms/protocol g p o o o

o

Route Information Protocol (RIP), Open Shortest Path First (OSPF), Border Gateway Protocol (BGP))

forwarding datagrams from incoming to outgoing link

Physical layer: bit-level reception Data D t link li k llayer: e.g., Ethernet

Connecting router’s input ports to its output ports - Executing routing protocol - Maintaining routing information and forwarding tables -Performing network management functions Network Layer

Three types of switching fabrics

Network Layer

Switching Via Memory First generation routers: o traditional computers with switching under direct control of f CPU ((routing gp processor)) o input and output ports functioned as traditional I/O devices in OS o Packet is copied from input port into system’s memory o Then routing processor extracts destination address from header, header look up output port in forwarding table, and copy packet to output port’s buffer o speed limited by memory bandwidth o o

If memory bandwidth is B packets per second can be written into, or read from memory Overall forwarding throughput must be less than B/2

Input Port

Network Layer

o Decentralized switching: o given datagram dest., lookup output port using forwarding table in input port y memory o goal: complete input port processing at ‘line speed’ o q queuing: g if datagrams g arrive faster than forwarding rate into switch fabric

Memory y

Output Port

Ex. Cisco’s Catalyst y 8500 series switches

System Bus

Network Layer

Switching Via a Bus

Switching g Via An Interconnection Network

o Input ports transfer packet directly

o To overcome bandwidth limitation of

to output p port p over shared bus o Only one packet at a time can be transferred over bus

shared bus is to use more sophisticated interconnection network

Packet P k t is i queued d att input i t portt if bus b is i busy

o

o Crossbar switch is interconnection network consisting

o bus contention: switching g speed p

2n buses (n input ports and n output ports) o Cisco 12000 family switches use an interconnection network, providing up to 60 Gbps through switching fabric

limited by bus bandwidth o Cisco 5600 : switches packets over 32 Gbps bus

Network Layer

Output p Ports

o

Network Layer

Output p port p queueing q g

Buffering required when datagrams arrive from fabric

faster than the transmission rate o Scheduling discipline chooses among queued datagrams for transmission o o

First-Come-First-Served (FCFS) scheduling Weighted Fair Queuing (WFQ) : shares outgoing link fairly among g different ff end-to-end connections that have p packets queued for transmission Network Layer

o buffering when arrival rate via switch exceeds

output line speed

o

queueing (delay) and loss due to output port buffer overflow!

Network Layer

Input Port Queuing

The Internet Network layer y

o Fabric slower than input ports combined -> queueing

may occur at input queues o Head-of-the-Line (HOL) blocking: queued datagram at front of queue prevents others in queue from moving forward

Host, router network layer functions: Transport layer: TCP, UDP

Network layer

IP p protocol •addressing conventions •datagram format •packet handling conventions

Routing protocols •path selection •RIP, OSPF, BGP

forwarding f di table

ICMP protocol •error reporting •router “signaling”

Link layer physical layer

Network Layer

IP datagram format IP protocol version number header length in 32 bits octets (bytes) Min value is 5 Min. “type” of data max number rema n ng hops remaining (decremented at each router) upper layer protocol to deliver payload to (TCP=6, UDP=17) o

o o o

how much overhead with TCP? 20 bytes of TCP 20 bytes of IP = 40 bytes + app layer overhead

4 bits

4 bits

32 bits

8 bits

16 bits type of ver head. len service Datagram length 3 bits fragment 16-bit identifier flgs 13 bits offset time to upper 16 bits header 8 bits 8 bits layer live checksum

MTU = Maximum Transmission Units

total datagram length (bytes) for fragmentation/ reassembly

32 bit source IP address 32 bit destination IP address Options (if any)

data (variable length, length typically a TCP or UDP segment)

Network Layer

E.g. timestamp, record route taken, specify l list of f routers to visit.

Network Layer

IP F Fragmentation gm & Reassembly m y o network links have MTU ((max.transfer size)) largest possible link-level frame. o different link types, different MTUs o large IP datagram divided ((“fragmented”) fragmented ) within net o one datagram becomes several datagrams o “reassembled” “ bl d” only l att final destination o IP header bits used to identify, order related fragments

fragmentation: in: one large datagram out: 3 smaller datagrams

reassembly

IP datagram Header

MTU

Token Ring (16 Mbps) – 17,914 bytes T k n Ring Token Rin (4 Mbps) - 4,464 4 464 bytes b t s Ethernet - 1,500 bytes Point-to-Point Protocol (PPP)–296 bytes Network Layer

Trailer

IP F Fragmentation gm and Reassembly m y Example o 4000 byte d datagram o MTU = 1500 bytes

o Communication at network layer is host-to-host

length ID fragflag offset =4000 =x =0 =0

o Computer mp somewhere m in the world need to

One large datagram becomes several smaller datagrams

1480 bytes in data field offset = 1480/8

Network Layer : Logical Addressing

length ID fragflag offset =1500 =x =1 =0 length ID fragflag offset =1500 =x =1 =185 length ID fragflag offset =1040 =x =0 =370

communicate with another computer somewhere else in the world through Internet o Packet P k transmitted i db by sending di computer may pass through several LANs or WANs before reaching destination computer o We need a global addressing scheme called logical

addressing

IP address to mean a logical address in network layer of TCP/IP protocol suite

o Today, we use the term

Network Layer

IP Addresses

Network Layer

IPv4 Addressing: g introduction

o The Internet address are 32 bits in length g o Address space is 232 or 4,294,967,296

o These addresses are referred to as IPv4 (IP version 4) addresses or simply IP address

o The need for more addresses motivated a new d design of f the h IP P layer l called ll d new generation of f IP P or IPv6 (IP version 6) o The Internet u uses 128-bit addresses that g give much mu greater flexibility in address location o These addresses are referred to as IPv6 (IP version 6) address Network Layer

o IPv4 address: 32-bit identifier for host, host router interface o interface: connection between host/router and physical link

223.1.1.1 gateway

223.1.1.2 223.1.1.4 223.1.1.3

223 1 2 1 223.1.2.1

223.1.2.9

223.1.3.27

223 1 2 2 223.1.2.2

o router’s router s typically have 223.1.3.2 223.1.3.1 multiple interfaces o host typically has one interface o IP addresses associated with each 223.1.1.1 = 11011111 00000001 00000001 00000001 interface 223

1

1

Network Layer

1

IP Addresses

“class“class -full” addressing:

given i notion ti of f ““network”, t k” let’s l t’ re-examine i IP addresses: dd

Classes of f IP Address

class A

0 network

B

10

C

110

D

1110

1.0.0.0 to 127 255 255 255 127.255.255.255

host

network

128.0.0.0 to 191.255.255.255

host

network t k multicast address

32 bits

h t host

192.0.0.0 to 223.255.255.255

Class

224.0.0.0 to 239.255.255.255

A

B

C Network Layer

Address for Private Networks

Network Octets (blanks in the IP dd are address used for octets identifying hosts) 0.__.__.__ to 127.__.__.__

Total Number of Possible Networks or Licenses 128

128.0.

8.0.__.__ . to 191.255.__.__

64x256 6 x 56

192.0.0.__ 192 0 0 to 223.255.255.__

32x256x256

16,384

2,097,152

Host Octets (blanks in IP address dd are used for octets identifying networks) __.0.0.1 to __.255.255.254

Total Number of Possible IP Add Addresses iin Each Networks

__.__.0. . .0.1 to __.__.255.254

65,534 65,53

__.__.__.1 1 to __.__.__.254

254

16,777,214

Network Layer

Subnets o IP address: o subnet part (high order bits) o host part (low order bits)

o What’s a subnet ?

o device interfaces with same subnet part of IP address o can physically reach each other without intervening router

223.1.1.1 223.1.1.2 223.1.1.4 223.1.1.3

223 1 2 1 223.1.2.1 223.1.2.9

223.1.3.27

223 1 2 2 223.1.2.2

subnet 223.1.3.2

223.1.3.1

network consisting of 3 subnets Class C

Network Layer

Network Layer

Subnets

223.1.1.0/24

223.1.2.0/24

Subnets

223.1.1.2

How many?

o Recipe

223.1.1.1

o To determine the

223.1.1.4 223.1.1.3

subnets, detach each interface from its host or router, creating islands of i l isolated d networks. k Each isolated network is called a subnet.

223.1.9.2

223.1.9.1 223.1.8.1 223.1.3.0/24

Subnet mask: /24

2 223.1.7.0 X

2 223.1.8.0 X

223 1 2 6 223.1.2.6 223.1.2.1

223 1 3 27 223.1.3.27 223.1.2.2

223.1.3.1

Network Layer

IP addressing: g CIDR

Internet’s address assignment strategy

CIDR: Classless InterDomain Routing o o

(RFC 4632)

(pronounced cider)

Subnet portion of address of arbitrary length Address format: a.b.c.d/x, where x is # bits in subnet portion of address

Subnet addressing

subnet b t part

host part

11001000 00010111 00010000 00000000 200.23.16.0/23

Organization is typically assigned a block of contiguous address ISP'ss block ISP

11001000 00010111 00010000 00000000

200 23 16 0/20 200.23.16.0/20

Organization 0 Organization 1 Organization 2 ...

11001000 00010111 00010000 00000000 11001000 00010111 00010010 00000000 11001000 00010111 00010100 00000000 ….. ….

200.23.16.0/23 200.23.18.0/23 200.23.20.0/23 ….

Organization 7

11001000 00010111 00011110 00000000

Network Layer 200.23.30.0/23

223.1.7.1

223.1.3.2

Network Layer

IP addresses: how to g get one? o Q: How does host get IP address? o hard-coded by system admin in a file o Windows: Wi d s: o control-panel->network connections->properties o ->Internet >Internet Protocol (TCP/IP) o UNIX: /etc/rc.config o DHCP: Dynamic y Host Configuration g Protocol: dynamically get address from as server o “plug-and-play” o allow ll host h to dynamically d ll obtain b its IP P address dd f from network server when it joins network Network Layer

DHCP client-server scenario A 223.1.1.1

B

223.1.1.2 223.1.1.4 223.1.1.3 223.1.3.1

223.1.2.1

DHCP server 223.1.2.9

223.1.3.27

223.1.2.2 223.1.3.2

E

arriving g DHCP client needs address in this network

Network Layer

DHCP client-server scenario DHCP server: 223.1.2.5

DHCP discover src : 0.0.0.0, 68 dest.: 255.255.255.255,67 yiaddr: 0.0.0.0 0000 transaction ID: 654

arriving client

DHCP offer src: 223.1.2.5, 67 d t 255.255.255.255, dest: 255 255 255 255 68 yiaddrr: 223.1.2.4 transaction ID: 654 Lifetime: 3600 secs DHCP request

time

src: 0.0.0.0, 68 dest:: 255.255.255.255, 67 yiaddrr: 223.1.2.4 transaction ID: 655 Lifetime: 3600 secs DHCP ACK src: 223.1.2.5, 67 dest: 255.255.255.255, 68 yiaddrr: 223.1.2.4 t transaction ti ID: ID 655 Lifetime: 3600 secs

Network Layer

Network Layer

IP addresses: how to g get one?

Q: How does network get subnet part of IP addr? dd ?

A: gets allocated portion of its provider ISP’s address space ISP's block

11001000 00010111 00010000 00000000

200.23.16.0/20

Organization 0 Organization 1 Organization g 2 ...

11001000 00010111 00010000 00000000 11001000 00010111 00010010 00000000 11001000 00010111 00010100 00000000 ….. ….

200.23.16.0/23 200.23.18.0/23 200.23.20.0/23 ….

Organization 7

11001000 00010111 00011110 00000000

200.23.30.0/23

Network Layer

Hierarchical addressing: g route aggregation gg g Hierarchical addressing allows efficient advertisement of routing information: Fly-By-Night-ISP Fl B Ni ht ISP advertises d ti tto outside t id world ld th thatt it should Be sent any datagrams whose first 20 address bits match 200.23.16.0/20

Organization 0

Hierarchical addressing: more specific routes t s ISPs-R-Us ISPs R Us has a more specific route to Organization 1 Organization 0

200.23.16.0/23

200 23 16 0/23 200.23.16.0/23 Organization 1

200.23.18.0/23

Organization 2

200.23.20.0/23

Organization 7

. . .

. . .

Fly-By-Night-ISP

“Send me anything with addresses beginning 200.23.16.0/20”

Organization 2

200 23 20 0/23 200.23.20.0/23

Internet

Organization 7

. . .

Fly-By-Night-ISP Fly

By Night ISP

Internet

200.23.30.0/23

200.23.30.0/23 /

ISPs-R-Us

“Send me anything with addresses beginning 1 199.31.0.0/16” 1 0 0/16”

ISPs-R-Us

. . .

“Send me anything with addresses beginning 200.23.16.0/20”

Organization 1

200.23.18.0/23

“Send me anything with addresses beginning 199.31.0.0/16 or 200.23.18.0/23”

Network Layer

Network Layer

NAT: Network Address Translation

NAT: Network Address Translation

rest of Internet

local network (e.g., g home network) 10.0.0.0/24 10.0.0.4

10 0 0 1 10.0.0.1 10.0.0.2

138.76.29.7 10.0.0.3

All datagrams leaving local network have same single source NAT IP address: 138.76.29.7, 138 76 29 7 different source port numbers

Datagrams with source or destination in this network have 10.0.0.0/24 10 0 0 0/24 address for source, destination (as usual)

Network Layer

o Motivation: local network uses jjust one IP address as far as outside world is concerned: o range of f addresses dd nott needed d df from ISP ISP: just j t one IP address for all devices o can change addresses of devices in local network without notifying outside world o can change ISP without changing addresses of d i devices iin llocall network t k o devices inside local net not explicitly addressable, visible by outside world (a security plus). plus) Network Layer

NAT: Network Address Translation

NAT: Network Address Translation

Implementation: NAT router must: o

o

o

outgoing datagrams: replace (source IP address, port

#) of every outgoing datagram to (NAT IP address, new port #) o . . . remote clients/servers li / will ill respond d using i (NAT IP address, new port #) as destination address.

remember b (in (i NAT ttranslation l ti ttable) bl ) every (source (

IP address, port #) to (NAT IP address, new port #) translation pair

incoming datagrams: replace (NAT IP address, new port #) in dest fields of every incoming datagram with corresponding (source IP address, address port #) stored in NAT table

Network Layer

2: NAT router changes datagram source addr from 10.0.0.1, 3345 to 138 76 29 7 5001, 138.76.29.7, 5001 updates table 2

NAT translation table WAN side addr LAN side addr

1: host 10.0.0.1 s nds d sends datagram t m tto 128.119.40.186, 80

138.76.29.7, 5001 10.0.0.1, 3345 …… ……

S: 10.0.0.1, 3345 D: 128.119.40.186, 80

S: 138.76.29.7, 5001 D: 128.119.40.186, 80

138.76.29.7 S: 128.119.40.186, 128 119 40 186 80 D: 138.76.29.7, 5001

3: Reply arrives dest. address: 138 76 29 7 5001 138.76.29.7,

3

1

10.0.0.1

10 0 0 4 10.0.0.4 S: 128.119.40.186, 80 D: 10.0.0.1, 3345

10.0.0.2

4

10.0.0.3 4: NAT router changes datagram dest addr from 138.76.29.7, 5001 to 10.0.0.1, 3345 Network Layer

Address Mapping

N t Network k L Layer Part II Computer Networks

o The delivery of a packet to a host or a router

requires two levels of addressing: logical address and physical address o We need to be able to map a logical address to its corresponding physical address and vice versa. o Mapping Logical Address to Physical Address can be done by y Address Resolution Protocol (ARP) : RFC 826 Logical address

Physical address

Network Layer

Address Resolution Protocol (ARP)

Network Layer

ARP Packet Type of network - Ethernet = 1

IPv4 = 080016

Length g of physical p y address in bytes - For ethernet value is 6 Length of logical address in bytes - For IPv4 protocol value is 4 This field is all 0s because Sender does not know Physical address of target

ARP Operation

Network Layer

Network Layer

Example

Network Layer

Internet Control Message Protocol (ICMP) o IP provides unreliable and connectionless datagram delivery y o IP protocol is a best-effort delivery service that delivers datagram from original source to final destination o Two deficiencies o Lack of error control o No error error-reporting reporting or error error-correcting correcting mechanism o Lack of assistance mechanism for host and management queries o Host sometimes needs d to d determine if f router or another host is alive o Sometimes a network administrator needs information from another host or router Network Layer

Network Layer

ICMP : Type of Messages o RFC 792 o ICMP message are divided into two broad categories o Error-reporting p g message g o Report problems that a router or host (destination) may encounter when it processes an IP packet k o Query message o Help H l h hostt or network t k manager gett specific ifi information from router or another host o Ex. Nodes can discover their neighbors o Hosts can discover and learn about routers on their network Network Layer

ICMP : Error Reporting

ICMP : Message Format o ICMP message has 8-byte header and variable-size

data section

o ICMP always reports error messages to original

source.

First 4 bytes are common to all

specific for each h message type t

o In error messages carries information for finding original packet that had error o In query messages data section carries extra information based on type of query Network Layer

Redirection Concept

Type 3 3 3 3 3 3 4 11 12

Code 0 1 2 3 6 7 0 0 0

description dest. network unreachable dest host unreachable d t protocol dest t l unreachable h bl dest port unreachable dest network unknown dest host unknown source quench (congestion control - not used) TTL expired Network Layer bad IP header

ICMP : Error Reporting (continued) o All error messages contain data section that includes o IP header of the original datagram plus o the first 8 bytes of data in that datagram Segment g

o Host A wants to send a datagram to host B o Router R2 is obviously most efficient routing choice, choice but host A o o o o

did not choose router R2 Datagram goes to R1 instead Router R1, after consulting its table, finds that packet should have gone to R2 R1 sends p packet to R2 and,at , the same time,, sends a redirection message to host A Host A’s routing table can now be updated Network Layer

Protocol (upper layer) : ICMP = 1

Port No. (UDP, TCP) (16 + 16 bits) Sequence No (TCP) (32 bits)

o network-layer t k l “above” “ b ” IP IP: o ICMP messages carried in IP datagramsNetwork Layer

ICMP : Error Reporting (continued)

ICMP : Error Reporting (continued)

o Destination Unreachable Message

o Source Quench Message o gateway have no buffer space to queue datagram o datagrams arrive too fast to be processed. processed o source quench message is request to host to cut back rate at which it is sending traffic to destination until it no longer receives source quench messages from the gateway

o o

Type yp = 3 Code o 0 = network unreachable; o 1 = host unreachable; o 2 = protocol unreachable; o 3 = port unreachable; o 4 = fragmentation g needed;; o 5 = source route failed.

Internet Header + 64 bits of Data Datagram

Network Layer

Network Layer

ICMP : Error Reporting (continued)

ICMP : Error Reporting (continued)

o Time Exceeded Message (TTL expired)

o Parameter Problem Message

Type = 12 Internet Header + 64 bits of Data Datagram o Code o 0 = Pointer indicates error o

Internet Header + 64 bits of Data Datagram o o

o o

Type = 11 Code o 0 = time to live exceeded in transit; o 1 = fragment reassembly time exceeded;

Pointer identifies octet of original datagram’s header where error was detected d t t d o For example, o 1 indicates something is wrong with Type of Service o 20 indicates i di t something thi is i wrong with ith type t code d of f first fi t option ti o

Code 0 may y be received from a gateway. g y Code 1 may be received from a host.

Network Layer

Network Layer

ICMP : Error Reporting (continued) o Redirect Message

address of gateway to which traffic for network specified in destination network field of original datagram’s data should be sent

ICMP : Query Type 0 8 9 10

Code 0 0 0 0

description echo reply (ping) q (p (ping) g) echo request route advertisement router discovery

o Query message is encapsulated in IP packet, which in Internet Header + 64 bits of Data Datagram

Type yp = 5 o Code o 0 = Redirect datagrams for Network o 1 = Redirect datagrams g for Host o 2 = Redirect datagrams for Type of Service and Network o 3 = Redirect datagrams for Type of Service and Host o

turn is encapsulated in data link layer frame o In this case, case no bytes of original IP are included in message

Network Layer

Echo-request q and echo-reply p y messages g

Network Layer

Route discovery and Route Advertisement o Route discovery

o Route advertisement

Ranking 0 – default 8000000016

Network Layer

Network Layer

Ping o Ping program is used to find whether a host 56+8 bytes of ICMP header + 20 bytes of IP header

56+8 bytes of ICMP hea ader

is alive or not

Network Layer

“Real” Internet delays y and routes o What do “real” Internet delay y & loss look like? o Traceroute program (tracert for windows) : provides delay measurement from source to router along end end-end end Internet path towards destination.

For all i: o sends three packets that will reach router i on path towardss destination towar st nat on o router i will return packets to sender o sender times interval between transmission and reply.

3 probes

3 probes 3 probes TTL=1

TTL=2

TTL=3

TTL 4 TTL=4

TTL=5 Network Layer

Traceroute o Source sends series of UDP segments to dest o First has TTL =1 o Second has TTL=2, etc. o Unlikely port number o When nth datagram arrives to nth router: o Router discards datagram o And sends to source an ICMP message (type 11, code 0) : TTL expired o Message includes name of router& IP address

o When ICMP message

o o o o

o

arrives, source calculates RTT Traceroute does d this h 3 times Stopping criterion UDP segment eventually arrives at destination host Destination returns ICMP “host unreachable” packet ((type yp 3, code 3 : Destination Port Unreachable) When source gets this ICMP, stops.

Network Layer

“Real” Internet delays y and routes traceroute: gaia.cs.umass.edu to www.eurecom.fr Three delay measurements from gaia.cs.umass.edu to cs-gw.cs.umass.edu 1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms 2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms 3 cht-vbns.gw.umass.edu g ((128.119.3.130)) 6 ms 5 ms 5 ms 4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms 5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms 6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms 7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms trans-oceanic 8 62.40.103.253 ((62.40.103.253)) 104 ms 109 ms 106 ms link 9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms 10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms 11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms 12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms 13 nice.cssi.renater.fr ((195.220.98.102)) 123 ms 125 ms 124 ms 14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms 15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms 16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms 17 * * * * means no response p (probe (p lost, router not replying) p y g) 18 * * * 19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms Network Layer

IPv6

Internet Protocol, version 5 (IPv5) o IPv5 was assigned to an experimental protocol

o Initial motivation: 32-bit address space soon

to be b completely l l allocated. ll d o Additional motivation: o o o o o

o

header format helps l speed processing/forwarding / header changes to facilitate QoS IPv6 datagram format: fixed-length 40 byte header no fragmentation allowed

o

o o

called Internet Stream Protocol (ST) Internet Stream Protocol (ST) was created for experimental transmission of voice, voice and video Two decades later, ST protocol was revised to get implemented p become ST2 and started to g into commercial projects by groups like IBM, NeXT, Apple, and Sun ST and ST+ offered connections, instead of its connection-less IPv4 counterpart ST also l guaranteed d QoS Q S

Network Layer

Network Layer

IPv4 & IPv6 Header Comparison

IPv6 Header (Cont) -Used for packet labelling, End-to-end QoS. RFC 6437.

- QoS management - Originally O i i ll created d for f giving i i realtime l i applicatins li i - special service, but currently unused (concept of “flow” not well defined)

Used for QoS. Like Type yp of Service (TOS) field in IPv4.

RFC 2474

Length of payload following header in bytes. Limits packet size to 64 KB. IPv6 source address

IPv6 destination address

Version

Traffic Class

Flow Label

(4 bits)

(8 bits)

(20 bits)

Payload Length (16 bits)

Next Header

IHL

(8 bits)

Source Address ((128 bits))

Code C d for f following f ll i extension t i header or Upper Layer protocol.

Like protocol type field in IPv4.

(TCP=6, UDP=17)

IPv6 Header

Type of Service

Total Length Version

Identification

Hop Limit

(8 bits)

Version

Time to Live

Protocol

Flags

Traffic Class

Flow Label

Fragment Offset

Header Checksum

Payload Length

Next Header

Hop Limit

Source Address D ti ti Address Destination Add

Number of hops until the packet gets discarded.

TTL in IPv4.

Destination Address

Options

Lege end

IP version. version Always 6 6.

IPv4 Header

(128 bits) Network Layer

Padding

- field’s name kept from IPv4 to IPv6 - fields not kept p in IPv6

Source Address

Destination Address

- Name & position changed in IPv6 - New field in IPv6

Network Layer

Summary of Header Changes between IPv4 & IPv6 o Streamlined o Fragmentation fields moved out of base header o IP options moved out of base header

IP 6 header IPv6 h d

o Options allowed, but outside of header, indicated by “Next Header” field

o o o

Extension Headers

Header Checksum eliminated Header Length field eliminated Length field excludes IPv6 header

o Revised o Time to Live Hop Limit o Protocol Next Header o Precedence P d & Type of f Service(TOS) ( ) Traffic ff Class l o Addresses increased 32 bits 128 bits o Extended o Flow Label field added

TCP header h d + data d t

next header = TCP

IPv6 header

Routing header

nnext xt header h d = Routing

n xt header next h d = TCP

TCP header + data

IPv6 header

Routing header

Fragment header

next header = Routing ut ng

next header = Fragment Fragm nt

next header = TCP

fragment of TCP header + data

Network Layer

Transition Trans t on From IPv4 To IPv6 o Not all routers can be upgraded simultaneous o no “flag days” o How will the network operate p with mixed IPv4 and IPv6 routers? o

Network Layer

Tunneling g Logical view:

Physical view:

E

F

IPv6

IPv6

IPv6

A

B

E

F

IPv6

IPv6

IPv6 P 6

IPv6

A

B

IPv6

tunnel

IPv4

IPv4

Tunneling: IPv6 carried as payload in IPv4 d datagram among IP IPv4 4 routers

Network Layer

Network Layer

Tunneling g Logical view:

Physical view:

A

B

IPv6

IPv6

A

B

C

IPv6

IPv6

IPv4

Flow: X Src: A Dest: F data

A-to-B: IPv6

E

F

IPv6

IPv6

D

E

F

IPv4

IPv6 P 6

IPv6

tunnel

Src:B Dest: E

Src:B Dest: E

Flow: X Src: A Dest: F

Flow: X Src: A Dest: F

data

data

B t C: B-to-C: IPv6 inside IPv4

B-to-C: B t C IPv6 inside IPv4

Flow: X Src: A Dest: F data

IPv6 address formats o IPv6 address size is 128 bits

(8 x 16 bits).

xxxx :xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx xxxx xxxx xxxx xxxx xxxx xxxx xxxx Where each x is a hexadecimal digit representing 4 bits

o IPv6 addresses range 0000:0000:0000:0000:0000:0000:0000:0000

E to F E-to-F: IPv6

ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff

Network Layer

Network Layer

IPv6 address formats

IPv6 address formats

o IPv6 addresses may be specified in two other

o An alternative format for IPv6 addresses

shortened formats: o Omit leading zeros

1050:0000:0000:0000:0005:0600:300c:326b 1050:0:0:0:5:600:300c:326b

o D Double bl colon l (::) o using double colons (::) in place of a series of zeros. ff06 0 0 0 0 0 0 3 ff06:0:0:0:0:0:0:c3 ff06::c3 o

Double colons may be used only once in an IP Network Layer address.

combines the colon and dotted notation o IPv4 address may be embedded in IPv6 address

o Hexadecimal values are specified p for left-most 96

bits, and decimal values are specified for rightmost 32 bits indicating the embedded IPv4 address. address IPv4

96 bits

32 bits

o This format ensures compatibility between IPv6

nodes and IPv4 nodes when y you are working g in mixed network environment.

Network Layer

IPv6 address formats o Two types of IPv6 addresses use this alternative format: o IPv4–mapped IPv6 address o o o

Used to represent IPv4 nodes as IPv6 addresses. allowing IPv6 applications to communicate directly with IPv4 applications Example, 0:0:0:0:0:ffff:192.1.56.10 and ::ffff:192.1.56.10/96 (shortened format)

o IPv4–compatible IPv6 address o used for tunneling. o allowing IPv6 nodes to communicate across IPv4 infrastructure o Example, 0:0:0:0:0:0:192 1 56 10 and ::192.1.56.10/96 0:0:0:0:0:0:192.1.56.10 ::192 1 56 10/96 (shortened format)

Routing Rout ng Algor Algorithms thms o Link state o Ex. Open Shortest Path First (OSPF)

routing algorithm

local forwarding table header value output link

o Distance Vector value in arriving o Ex. Routing packet’s header Information Protocol (RIP)

0100 0101 0111 1001

3 2 2 1

1

0111

3 2

Network Layer

Graph abstract abstraction on

Network Layer

Graph abstraction: abstract on costs

5 2

u

2 1

Graph: G = (N,E)

v

x

5 3

w 3

1

5

z

1

y

2

u

2 1

2

N = set off routers = { u, v, w, x, y, z } E = set of links ={ (u,v), (u,x), (v,x), (v,w), (x,w), (x,y), (w,y), (w,z), (y,z) } Remark: Graph abstraction is useful in other network contexts Example: P2P, P2P where N is set of peers and E is set of TCP connections Network Layer

v

x

• c(x,x c(x,x’)) = cost of link l nk (x,x’) (x,x )

3

w 3

1

5

z

1

y

- e.g., c(w,z) = 5

2

• cost c st c could uld always l s be 1, 1 orr inversely related to bandwidth, or inversely related to g congestion

Cost of path (x1, x2, x3,…, xp) = c(x1,x2) + c(x2,x3) + … + c(xp-1,xp) Question: What’s the least-cost path between u and z ?

Routing algorithm: algorithm that finds least-cost least cost path Network Layer

A Link-State Routing Algorithm

Routing g Algorithm g m classification f o Global or decentralized

information? o Global: o all routers have complete topology, link cost information o “link state” algorithms o Decentralized: o router knows physicallyconnected neighbors, link costs t tto neighbors i hb o iterative process of computation, exchange of info f with h neighbors h o “distance vector” algorithms

5

o Static or dynamic? o Static: o routes change slowly over time

o Dynamic:

Dijsktra’s D j Algorithm g m

o routes change more quickly o periodic update o in response to link costt changes h

o Dijkstra’s algorithm o net topology, link costs known to all nodes o accomplished via “link state broadcast” o all nodes have same info o computes least cost paths from one node (‘source”) to all other nodes o gives forwarding table for that node o iterative: after k it iterations, ti s k know lleast st cost st path to k dest.’s

u 1

2

v

3

w

u 2 1 1 Initialization: 3 1 2 N N' = {u} x y 3 for all nodes v 1 4 if v adjacent to u Cost U Node 5 then D(v) = c(u,v) c(u v) 6 else D(v) = 7 node cost 8 Loop p 9 find w not in N' such that D(w) is a minimum 10 add w to N' 11 update D(v) for all v adjacent to w and not in N' : 12 D(v) = min( D(v), D(w) + c(w,v) ) 13 /* new cost to v is either old cost to v or known 14 shortest path cost to w plus cost from w to v */ 15 until til all ll nodes d in i N'

v 2

3

w

x to y; = neighbors

5

1

3

x 1 y o Notation: o c(x,y): c(x y): link li k costt f from node d

z

2

if not direct

o D(v): D( ) current value of cost of path from source to dest. v

o p(v): predecessor node

along path from source to v

o N N':: set of nodes whose

least cost path definitively known Network Layer

Network Layer

5

2

Dijkstra’s D j algorithm: g m example mp

5

z 2

Network Layer

N’

Step 0 1 2 3 4 5

N' u ux uxy uxyv uxyvw uxyvwz

D(v),p(v) D(w),p(w) 2 2,u 5 5,u 2,u 4,x 2,u 3,y 3y 3,y

D(x),p(x) 1 1,u

D(y),p(y)

D(z),p(z)

2,x

5 2

u

v

3

2 1

x

Shortest Path

w 3

1

5

z

1

y

2

Node u

Node

Network Layer

4,y 4y 4,y 4,y

Dijkstra’s D j algorithm: g m example mp (2) ( ) Resulting shortest-path tree from u:

v

Bellman Ford Equation (dynamic programming) Bellman-Ford Define dx(y) := cost of least least-cost cost path from x to y

w

u

z x

y

Then

R Resulting l i f forwarding di table bl iin u: destination

link

v x

(u,v) (u v) (u,x)

y

(u,x)

w

(u x) (u,x)

z

(u,x)

dx(y) = min {c(x {c(x,v) v) + dv(y) } v where h min i is i ttaken k over all ll neighbors i hb v of fx Network Layer

Bellman-Ford Bellman Ford example 5 2

u

v 2

1

x

3

w 3

1

Distance D stance Vector Algor Algorithm thm

z

1

y

2

Distance Vector Algorithm g

Clearly dv(z) = 5, Clearly, 5 dx(z) = 3, 3 dw(z) = 3

5

Network Layer

B-F equation says: du(z) = min { c(u,v) + dv(z), c(u,x) + dx(z), c(u w) + dw(z) } c(u,w) = min {2 + 5, 1 + 3, 5 + 3} = 4

Node that achieves minimum is next h p in hop i shortest sh t st path p th f forwarding di ttable bl Network Layer

o Iterative, asynchronous: Each node: each local iteration caused by: wait for (change in local link o local link cost change g cost or msg from neighbor) o DV update message from neighbor recompute estimates o Distributed: o each node notifies if DV to anyy dest has neighbors only when its changed, notify neighbors DV changes o neighbors g then notify fy their neighbors if Network Layer necessary

0

7

z

x y 2 0 1 z node z table cost to x y z

time

Network Layer

x y z 71

0

from

from m

cost to x y z x 0 2 7 y 2 0 1 z 7 1 0 cost to x y z x 0 2 7 y 2 0 1 z 3 1 0

= min{2+1 , 7+0} = 3

x 0 2 3 y 2 0 1 z 3 1 0 costt to t x y z

from

1

frrom

frrom

from

x

2

y

x 0 2 3 y 2 0 1 z 7 1 0

Dx(z) = min{c(x,y) + Dy(z), c(x,z) + Dz(z)}

cost to x y z

x 0 2 3 y 2 0 1 z 3 1 0

x

2

y

1

7

cost to x y z from f

x y 2 0 1 z node z table cost to x y z x y z 71

x 0 2 7 y z node y table cost to x y z

cost to x y z

fro om

x 0 2 3 y 2 0 1 z 7 1 0

node x table cost to x y z from m

from m

from m

x 0 2 7 y z node y table cost to x y z

= min{2+1 , 7+0} = 3

cost to x y z

Dx(y) = min{c(x,y) + Dy(y), c(x,z) + Dz(y)} = min{2+0 , 7+1} = 2

from f

node x table cost to x y z

Dx(z) = min{c(x,y) + Dy(z), c(x,z) + Dz(z)}

from

Dx(y) = min{c(x,y) + Dy(y), c(x,z) + Dz(y)} = min{2+0 , 7+1} = 2

x 0 2 3 y 2 0 1 z 3 1 0 time

Network Layer

z

Chapter p 6 Wireless and Mobile Networks

Chapter hapt r 6 6: W Wireless r ss an and Mobile Mo Networks N twor s Background: o # wireless (mobile) phone subscribers now exceeds

# wired phone subscribers!

Part art I

o computer networks: laptops, palmtops, PDAs, smart

A note on the use of these ppt slides: We’re making g these slides freely y available to all ((faculty, y students, readers). ) They’re in PowerPoint form so you can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously represent a lot of work on our part. In return for use, we only ask the following: If you use these slides (e.g., in a class) in substantially unaltered form, th t you mention that ti th their i source ((after ft all, ll we’d ’d lik like people l to t use our book!) b k!)

If you post any slides in substantially unaltered form on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and note our copyright of this material.

Computer Networking: A Top Down Approach

5th edition.

Jim Kurose Kurose, Keith Ross Addison-Wesley, April 2009.

Thanks and enjoy! JFK/KWR All material copyright 1996-2009 J.F Kurose and K.W. Ross, All Rights Reserved

6: Wireless and Mobile Networks

Wireless o 6.2 6 2 Wireless Wi l ss li links, ks characteristics o

CDMA

o 6.3 IEEE 802.11

wireless LANs (“wi-fi”) o 6.4 Cellular Internet Access o o

architecture standards (e.g., (e g GSM)

o t two important im t t (b (butt diff different) t) challenges h ll s o wireless: communication over wireless link o mobility: y handling the mobile user who changes p point of attachment to network 6: Wireless and Mobile Networks

6-1

Chapter 6 outl outline ne 6.1 Introduction

phone, Internet-enabled phone promise anytime untethered Internet access

6-2

Elements of a wireless network

Mobility y o 6.5 Principles: addressing and routing to mobile users o 6.6 Mobile IP o 6.7 Handling mobility in cellular ll l networks t k o 6.8 Mobility and higherlayer y protocols p

network infrastructure

Wireless Hosts o laptop, PDA, IP phone o run applications o may be stationary ( (non-mobile) b l ) or mobile bl o wireless does not always mean mobility

6.9 Summary 6: Wireless and Mobile Networks

6-3

6: Wireless and Mobile Networks

6-4

Elements of a wireless network

Elements of a wireless network

Base Station

Wireless Link

o typ typically cally connected to

wired network o relay - responsible for sending packets b between wired i d network and wireless host(s) in its “area” o e.g., e g cell towers towers, 802.11 access points

network infrastructure

6: Wireless and Mobile Networks

o typ typically cally used to

network infrastructure

6: Wireless and Mobile Networks

6-5

Characteristics of selected wireless link standards

connect mobile(s) to base station o also used as backbone li k link o multiple access protocol coordinates link access o various data rates, transmission distance

6-6

Elements of a wireless network Infrastructure Mode

o base stat station on connects

Data rate (Mbps)

200 54 5-11

802.11n 802.11a,g

4 1

802.11a,g point-to-point

802.11b

data

802.16 (WiMAX) UMTS/WCDMA-HSPDA, CDMA2000-1xEVDO

3G cellular enhanced

network infrastructure

mobiles into wired network o handoff: mobile changes h base b station i providing connection into wired network

802.15

.384

3G

UMTS/WCDMA, CDMA2000

.056

2G

IS-95, CDMA, GSM

Indoor

Outdoor

10-30m 10 30m

50-200m 50 200m

Mid-range outdoor

Long-range outdoor

200m – 4 Km

5Km – 20 Km

6: Wireless and Mobile Networks

6-7

6: Wireless and Mobile Networks

6-8

Wireless network taxonomy

Elements of a wireless network Ad Hoc Mode o no base stat stations ons o nodes can only transmit to other nodes within link coverage o nodes organize themselves into a network: route among themselves

Multiple Hops

Single Hop Infrastructure (e.g., APs) Access Points

N No Infrastructure

h host connects to base station (WiFi, WiMAX, cellular) which connects to larger Internet no base b station, t ti no connection to larger Internet (Bluetooth, Ad hoc networks))

h st may host m have h ve to t relay through several wireless nodes to g connect to larger Internet: mesh net no base station, no connection to larger Internet. May have to relay to reach other a given wireless node MANET VANET MANET,

Mobile Ad hoc Networks

Wireless Link Characteristics (1)

o

o

o SNR: Signal-to-Noise Ratio

Decreased Signal Strength: radio signal attenuates as it propagates through matter (path loss)

o

Interference from other sources: standardized wireless network f frequencies ((e.g., 2.4 GHz) G ) shared h d by b other h devices d (e.g., ( phone); h ) devices (motors) interfere as well Multipath Propagation: radio signal reflects off objects ground, ground arriving ad destination at slightly different times

…. make communication across (even a p point to point) p wireless link much more “difficult” “d ff l ”

6: Wireless and Mobile Networks

6-10

Wireless Link W L Characteristics (2) ( )

Differences from wired link …. o

6: Wireless and Mobile Networks

6-9

6-11

o

larger SNR – easier to extract signal from noise (a “good thing”)

SNR versus BER tradeoffs o given physical layer:

o

increase power -> increase SNR >decrease BER SNR->decrease given SNR: choose physical layer that meets BER requirement giving highest requirement, throughput o SNR may change with mobility: dynamically adapt physical layer (modulation technique, rate)

10-1 10-2

Bit Error Ratte (BER)

6: Wireless and Mobile Networks

Vehicular Ad hoc Networks

10-3 10-4 10-5 10-66 10-7

10

20

30

40

SNR(dB) QAM256 (8 Mbps) QAM16 (4 Mbps) BPSK (1 Mbps) 6: Wireless and Mobile Networks

6-12

Wireless network characteristics Multiple M lti l wireless i l senders d and d receivers i create t additional dditi l problems (beyond multiple access): B

A

B

A

o unique “code” assigned to each user; i.e., code set

C

partitioning

C’s signal strength

A’s signal strength

Hidden terminal problem o B,, A hear each other o B, C hear each other o A, C can not hear each other means A, C unaware of their interference at B

space

Signal attenuation:

o B, B A hear h each h other h o B, C hear each other

o A, C can not hear each other

i t f i att B interfering

6: Wireless and Mobile Networks

code

d0 = 1

1 1 1

1 1 1 -1 -1 -1

slot 1

1 1 1 1 1 1 -1

-1 -1 -1

slot 0

M

Di = received input code

receiver M

Chips M=8

1 1 1 1 1 1

1 -1 -1 -1 1 1 1

1 1 1

1 -1

-1 -1 -1

-1 -1 -1

slot 1

1 -1

Z m=1 i,m

-1 -1 -1

slot 0 channel output

Sender 2

.c

m

M

1 -1

-1

6-14

Sender 1

1 -1

slot 1 channel output t t

1 -1

6: Wireless and Mobile Networks

CDMA: two-sender interference

1 -1 -1 -1

1 -1

own “chipping” sequence (i.e., code) to encode data o Encoded signal g = (original g data) X (chipping pp g sequence)) o Decoding: inner-product of encoded signal and chipping sequence o allows multiple users to “coexist” and transmit simultaneously with minimal interference (if codes are “orthogonal”)

channel output Zi,m

Zi,m= di.cm

d1 = -1

o all users share same frequency, but each user has

6-13

CDMA Encode/Decode sender

o used in several wireless broadcast channels

( ll l (cellular, satellite, t llit etc) t ) standards t d d

C

data bits

Code Division Multiple Access (CDMA)

-1 -1 -1

slot 0

d0 = 1 d1 = -1

slot 1 channel output

slot 0 channel output

Chipping Sequence 6: Wireless and Mobile Networks

6-15

6: Wireless and Mobile Networks

6-16

Chapter 6 outl outline ne 6.1 Introduction

Wireless and Mobile Networks

Wireless o 6.2 6 2 Wireless Wi l ss li links, ks characteristics o

o 6.3 IEEE 802.11

Part II

wireless LANs (“wi-fi”) o 6.4 cellular Internet access

September 6, 2013

o o 6: Wireless and Mobile Networks

IEEE 802.11 Wireless LAN o

802 11b 802.11b o o o

2.4 GHz unlicensed spectrum up to 11 Mbps Physical layer : direct sequence spread spectrum (DSSS) o all hosts use same chipping code

CDMA

o 802.11a o o

6-18

Orthogonal Frequency Division Multiplexing (OFDM) Regular FDM single carrier

5 GHz range up to 54 Mbps Physical Layer : OFDM

6.9 Summary 6: Wireless and Mobile Networks

6-17

Federal Communications Commission (FCC) Industrial, Scientific and Medical (ISM) radio bands • 902 to 928 MHz • 2.400 to 2.4835 GHz • 5.725 to 5.875 GHz

o

architecture standards (e.g., (e g GSM)

Mobility y o 6.5 Principles: addressing and routing to mobile users o 6.6 Mobile IP o 6.7 Handling mobility in cellular ll l networks t k o 6.8 Mobility and higherlayer y protocols p

OFDM

o 802.11g o o o

2.4 GHz range up to 54 Mbps Physical Layer : OFDM

o 802.11n: multiple antennae o o o

o o

2.4 / 5 GHz range up p to 200 Mbps p Physical Layer : OFDM

all use CSMA/CA for Multiple Access all have base-station and ad-hoc network versions

6: Wireless and Mobile Networks

6-19

6: Wireless and Mobile Networks

6-20

802.11: Channels, Association

802.11 LAN architecture o wireless host communicates

Internet

hub, switch or router

AP BSS 1

AP

BSS 2

with base station o Base Station = Access Point (AP) o Basic Service Set (BSS) (aka “cell”) in infrastructure mode contains: o wireless hosts o access point (AP): base station o Ad hoc mode: hosts only

6: Wireless and Mobile Networks

6-21

AP 1

BBS 2

1

1 2

AP 2

BBS 1

AP 1

1

3

2 3

AP 2 4

H1

H1

Passive Scanning:

Active Scanning:

(1) beacon frames sent from APs (2) association Request frame sent: H1 to selected AP (3) association Response frame sent: H1 to selected AP

(1) Probe Request frame broadcast from H1 (2) Probes response frame sent from APs (3) Association Request frame sent: H1 to selected AP (4) Association Response frame sent: H1 to selected AP 6: Wireless and Mobile Networks

different frequencies o AP admin chooses frequency q y for AP o interference possible: channel can be same as that chosen by neighboring AP!

o Host: m must associate with an AP o scans channels, listening for beacon frames containing AP’s name (SSID) and MAC address o selects AP to associate with o may perform authentication [Chapter 8] o will typically run DHCP to get IP address in AP’s subnet 6: Wireless and Mobile Networks 6-22

o Avoid collisions: 2+ nodes transmitting at same time

BBS 2

2

o 802.11b: 2.4GHz-2.485GHz spectrum divided into 11 channels at

IEEE 802.11: Multiple Access

802.11: 80 . Pass Passive/Active ve/Act ve scann scanning ng BBS 1

Note: Channel 14 is only allowed in Japan, Channels 12 & 13 are allowed in most parts of the world, except the USA, where only Channels 1 to 11 are legal to use.

6-23

o 802.11: CSMA - sense before f transmitting g o don’t collide with ongoing transmission by other node

o 802.11: no collision detection! o difficult diffi l to receive i ((sense collisions) lli i ) when h transmitting i i d due to weak received signals (fading) o can’t sense all collisions in any case: hidden terminal, fading o goal: avoid collisions: CSMA/C(ollision)A(voidance)

A

B

A

C B

C C’s signal strength

A’s signal strength space

6: Wireless and Mobile Networks

6-24

Timing in CSMA/CA

CSMA/CA procedure

o In wireless network, much of sent energy is lost in

transmission : not useful for effective collision detection o We need to avoid collisions on wireless network because they cannot be detected o CDMA/CA has three strategies o o o

InterFrame Space (IFS) Contention window Acknowledgement

Short Inter Frame space (SIFS) - 28 microseconds Point Coordination IFS (PIFS) - 78 microseconds Distributed IFS (DIFS) – 128 microseconds

25

Avoiding collisions (more)

IEEE 802.11 MAC Protocol: CSMA/CA

idea: allow sender to “reserve” reserve channel rather than random access of

802.11 sender Distributed Inter Frame Space e.g.128 microseconds 1 if sense channel h l idle idl for f DIFS then th sender receiver transmit entire frame (no CD) 2 if sense channel busy y then start random backoff time timer counts down while channel idle transmit when timer expires if no ACK, increase random backoff interval, repeat 2

DIFS

data

data frames: avoid collisions of long data frames small Request-to-Send (RTS) packets to BS using CSMA o RTSs may still collide with each other (but they’re short) o BS broadcasts Clear-to-Send CTS in response to RTS o CTS heard h d by all ll nodes d o sender transmits data frame o other stations defer transmissions o sender first transmits

SIFS

ACK

802.11 802 11 receiver i - if frame received OK return ACK after SIFS (ACK needed due to hidden terminal problem) Short Inter Frame Space e.g. 28 microseconds

26

6: Wireless and Mobile Networks

avoid data frame collisions completely using small reservation packets!

6-27

6: Wireless and Mobile Networks

6-28

Collision Avoidance: RTS-CTS exchange A

802.11 80 . frame frame: addressing address ng

B

AP

2

2

6

6

6

reservation collision

defer

time

6: Wireless and Mobile Networks

seq address 4 control

R1 router

6: Wireless and Mobile Networks

Internet

2

2

6

6

6

R1 MAC addr H1 MAC addr

2 Protocol version

source address

802.3 frame

2 Type

0 for 802.11 standard

AP MAC addr H1 MAC addr R1 MAC addr address 2

6-30

frame seq # (for RDT)

data, management, control t l

address 3

802.11 frame 6: Wireless and Mobile Networks

6-31

4

1

Subtype

To AP

6

2

frame address address address duration control 1 2 3 Set when frame is followed by other fragment

address 1

CRC

802.11 80 . frame frame: more

AP

dest. address

payload

Address 2: MAC address of wireless host or AP transmitting this frame

duration of reserved transmission time (RTS/CTS) H1

4

Address 3: MAC address of router interface to which AP is attached

6-29

802.11 80 . frame frame: addressing address ng

bytes

0 - 2312

Address 4: used only in ad hoc mode

Address 1: MAC address of wireless host or AP to receive this frame DATA (A)

6

2

frame address address address duration control 1 2 3

1

payload p y

Set in case of retransmission frame

1

From More AP frag

bit set when station go Power Save mode

1

4 bytes

0 - 2312

seq address 4 control t l

1

CRC

Wired Equivalent Privacy

1

Power More Retry mgt data

1

1

WEP

Rsvd

When set means that AP have more buffered data for a station in Power Save mode

Encryption and

frame type authentication 6: Wireless and Mobile are Networks used? 6-32 (RTS, CTS, ACK, data, Beacon, Association (request/response)

Frame type and sub type

Frame type and sub type

6: Wireless and Mobile Networks

Transmission between station’s in the same BSS

6: Wireless and Mobile Networks

6-33

Frame transmission coming from Distribution System

6-34

802.11: mobility within same subnet o H1 remains in same IP

subnet: IP address can remain same o switch: which AP is associated with H1?

Frame transmission designated for Distribution System y

Transmission designated to STA in other BSS, transmitted between AP trough Wireless Distribution System

6: Wireless and Mobile Networks

6-35

o

self-learning : switch will see frame from H1 and “remember” which switch port can be used to reach H1

router hub or switch BBS 1 AP P1 AP 2 H1

BBS 2

6: Wireless and Mobile Networks

6-36

802.15: Personal Area Network (Bluetooth)

802.11: advanced capabilities Rate Adaptation

10-1

o base b station, t ti mobile bil

QAM256 (8 Mbps) QAM16 (4 Mbps) BPSK (1 Mbps) operating point

(mouse, keyboard, headphones) o ad dh hoc: no infrastructure i f t t o master/slaves:

10-4 10-5 10-6 10-7

10

20

30

SNR(dB) ( )

40

o

1. SNR decreases, BER increase as node moves away from base station

o

Bluetooth specification o o

o

o

o WiMAX is short for

6: Wireless and Mobile Networks

Worldwide Interoperability for Microwave Access o like 802.11 & cellular: base station model o transmissions t nsmissi ns tto/from /f m base station by hosts with omnidirectional antenna o base station-to-base station to base station backhaul with point-to-point antenna o unlike 802.11: 802 11: o range ~ 6 miles (9.654 km) (“city rather than coffee shop�)) shop o ~14 Mbps 6-40

P

S P

radius of coverage

M S

P

S

P

M Master device S Slave device P Parked device (inactive) 6: Wireless and Mobile Networks

IEEE 802.16: WiMAX

o Whenever there is a

o

2.4-2.5 GHz radio band up to 721 kbps

6-37

Bluetooth

o

slaves request permission to send (to master) master grants requests

o 802.15: 802 15: evolved from

2. When BER becomes too high, switch to lower transmission transm ss on rate but w with th lower BER 6: Wireless and Mobile Networks

connection between two Bluetooth devices, a piconet is formed Always 1 master and up to 7 active slaves Any Bluetooth device can be either a master or a slave Can be a master of one piconet and a slave of another piconet at the same time (scatternet) All devices have the same timing and frequency hopping sequence

Limited to 7 Active slaves for each master

o replacement p m for f cables

10-2 10-3

BER

dynamically change transmission rate (physical layer modulation technique) as mobile moves moves, SNR varies

o less than 10 m diameter

1

= 1.609344

6-39

point-to-point

point-to-multipoint

6: Wireless and Mobile Networks

6-41

Components of cellular network architecture

Chapter 6 outl outline ne 6.1 Introduction Wireless o 6.2 6 2 Wireless Wi l ss li links, ks characteristics o

CDMA

o 6.3 IEEE 802.11

wireless LANs (“wi-fi”) o 6.4 Cellular Internet Access o o

architecture standards (e.g., (e g GSM)

MSC

Mobility y o 6.5 Principles: addressing and routing to mobile users o 6.6 Mobile IP o 6.7 Handling mobility in cellular ll l networks t k o 6.8 Mobility and higherlayer y protocols p

connects cells to wide area net manages call setup (more later!) handles mobility (more later!)

cell

covers geographical region base station (BS) analogous to 802.11 AP mobile users attach t n to network t k th through h BS

Mobile Switching Center

air-interface:

physical and link layer protocol between p mobile and BS

Mobile Switching Center

6.9 Summary 6: Wireless and Mobile Networks

Public telephone network and network, Internet

wired network 6: Wireless and Mobile Networks

6-43

Cellular networks: networks the first f rst hop

Cellular standards: standards brief br ef survey

Two techniques for sharing mobile-to-BS bil t BS radio di spectrum o combined FDMA/TDMA FDMA/TDMA: divide spectrum in frequency channels, divide each channel into time slots frequency bands o CDMA: code division multiple access

2G systems: voice channels

6-44

o IS-136 TDMA: combined FDMA/TDMA (north

america) o GSM (global system for mobile communications): combined FDMA/TDMA

time slots

o

most widely deployed

o IS-95 CDMA: code division multiple access

GSM

6: Wireless and Mobile Networks

6-45

Don’t drown in a bowl of alphabet soup: use this f reference for f only l 6: Wireless and Mobile Networks

6-46

Cellular standards: standards brief br ef survey

Cellular standards: standards brief br ef survey

2.5 G systems: voice and data channels

o 3G systems: voice/data o Universal Mobile Telecommunications Service (UMTS) ( )

o for those who can’t wait for 3G service: 2G extensions o g general packet p radio service ((GPRS)) o evolved from GSM o data sent on multiple channels (if available) o Data rates 56-114 kbps o enhanced data rates for global evolution (EDGE) o also evolved from GSM, using enhanced modulation o data rates up to 384K

o o o

o CDMA-2000 (phase 1) o data rates up to 144K o evolved from IS-95

o 6: Wireless and Mobile Networks

144 kbps 384 kbps p 2 Mbps

‌.. more (and more interesting) cellular topics due to mobility (stay tuned for details)

6-47

RTT= Radio Telephone Technology 1xRTT = 1.25 MHz 3xRTT R = 3.75 5 MHz H

CDMA2000

data service: High Speed Uplink/Downlink packet Access (HSDPA/HSUPA): 3 Mbps o CDMA CDMA-2000: 2000 CDMA in TDMA slots o data service: 1xEvlution Data Optimized (1xEVDO) up to 14 Mbps o o

6: Wireless and Mobile Networks

6-48

6: Wireless and Mobile Networks

6-50

3G

WCDMA

6: Wireless and Mobile Networks

Time-Division Synchronous CDMA (TD-SCDMA)

6-49

Chapter 6 outl outline ne

What iss mobility? mob l ty?

6.1 Introduction

o spectrum p of f mobility, y, from f the

Wireless o 6.2 6 2 Wireless Wi l ss li links, ks characteristics o

CDMA

o 6.3 IEEE 802.11

wireless LANs (“wi-fi”) o 6.4 Cellular Internet Access o o

architecture standards (e.g., (e g GSM)

Mobility y o 6.5 Principles: addressing and routing to mobile users o 6.6 Mobile IP o 6.7 Handling mobility in cellular ll l networks t k o 6.8 Mobility and higherlayer y protocols p

no mobility y

“home” of f mobile

(e.g., 128.119.40/24)

mobile user, passing through multiple access point while maintaining ongoing connections (like cell phone)

6: Wireless and Mobile Networks

6-51

6-52

Mobility: Mob l ty more vocabulary

Mobility: Mob l ty Vocabulary home network: permanent

high h gh mobility mob l ty

mobile wireless user, mobile user, using same access connecting/ point disconnecting from network using DHCP.

6.9 Summary 6: Wireless and Mobile Networks

network p perspective: p

home agent: entity that will perform mobility functions on behalf of mobile, when mobile is remote

Permanent address: remains constant (e.g., 128.119.40.186)

visited network: network

in which mobile currently y resides (e.g., 79.129.13/24)

Care-of-address: Care of address address in visited network. (e.g., 79,129.13.2)

Permanent address:

address in home network, can always be used to reach mobile e.g., 128.119.40.186

wide area network

wide area network

correspondent

6: Wireless and Mobile Networks

6-53

correspondent: wants to communicate with mobile

fforeign i n agent: nt: entity ntit in visited network that performs mobility functions on behalf of mobile.

6: Wireless and Mobile Networks

6-54

Mobility: Mob l ty approaches

How do y you contact a mobile friend: Consider friend frequently changing addresses, how do you find her?

I wonder won r wh where r Alice moved to?

o

o search all p phone

books? o call her parents? o expect her h to let l you know where he/she is?

o

Let routing g handle it: routers advertise p permanent

address of mobile-nodes-in-residence via usual routing table exchange. o routing tables indicate where each mobile located o no changes to end-systems

Let end end-systems systems handle it: o indirect routing: communication from

o

6: Wireless and Mobile Networks

o

visited network

home network

not address of mobile-nodes-in-residence via usual scalable routing table exchange. to millions of o routing tables indicate mobiles where each mobile located o no changes to end-systems

let end end-systems systems handle it: o indirect routing: communication from

1

2

wide id area network

foreign forei n agent a ent contacts home agent home: “this mobile is resident in my network�

correspondent to mobile goes through home agent, then h forwarded f d d to remote direct routing: correspondent gets foreign address of mobile mobile, sends directly to mobile 6: Wireless and Mobile Networks

6-56

Mobility: y registration g

Let routing g handle it: routers advertise p permanent

o

6: Wireless and Mobile Networks

6-55

Mobility: Mob l ty approaches o

correspondent to mobile goes through home agent, then h forwarded f d d to remote direct routing: correspondent gets foreign address of mobile mobile, sends directly to mobile

mobile contacts foreign agent on entering visited network

End result: o Foreign g agent g knows about mobile o Home agent knows location of mobile 6-57

6: Wireless and Mobile Networks

6-58

Mobility y via Indirect Routing g

Indirect Routing: g comments mm

foreign agent packets,, receives p forwards to mobile

home agent intercepts packets, forwards to foreign agent

home network

o Mobile uses two addresses: visited network

3 wide area network

p correspondent addresses packets using home address of mobile

1

2

4 mobile replies directly to correspondent p 6: Wireless and Mobile Networks

permanent m t address: dd ss: used s d by b correspondent s d t (hence (h mobile location is transparent to correspondent) o care-of-address: f used by u y home m agent g to forward f w datagrams to mobile o foreign agent functions may be done by mobile itself o triangle routing: correspondent-home-networkmobile o inefficient when o correspondent, mobile o are in same network o

6: Wireless and Mobile Networks

6-59

Indirect Routing: g moving g between networks

Mobility y via Direct D Routing g

o suppose mobile user moves to another

network t k o o o o

correspondent forwards to foreign agent

registers with new foreign agent new foreign agent registers with home agent home agent update care-of-address for mobile packets continue to be forwarded to mobile (but with new care-of-address)

p correspondent requests, receives foreign address of mobile

maintained!

6-61

visited network

4 wide area network

2

transparent: on going connections can be

6: Wireless and Mobile Networks

foreign agent receives p packets,, forwards to mobile

home network

o mobility, changing foreign networks

6-60

1

3

4 mobile replies directly to correspondent p

6: Wireless and Mobile Networks

6-62

Mobility y via Direct Routing: g comments

Accommodating g mobility y with direct routing g o anchor foreign agent: FA in first visited network

o overcome triangle routing problem

o data always y routed first to anchor FA

o non-transparent to correspondent:

o when mobile moves: new FA arranges to have data

correspondent must get care-of-address from home agent o

forwarded from old FA (chaining)

what if mobile changes visited network?

foreign net visited at session start

wide area network

anchor foreign agent

1

2 4 5

correspondent 6: Wireless and Mobile Networks

correspondent agent

3 new foreign agent

new foreign networkk

6: Wireless and Mobile Networks

6-63

Chapter 6 outl outline ne

Mobile Mob le IP

6.1 Introduction

o RFC 3344 : IP Mobility Support for IPv4

Wireless o 6.2 6 2 Wireless Wi l ss li links, ks characteristics o

CDMA

o 6.3 IEEE 802.11

wireless LANs (“wi-fi�) o 6.4 Cellular Internet Access o o

architecture standards (e.g., (e g GSM)

Mobility y o 6.5 Principles: addressing and routing to mobile users o 6.6 Mobile IP o 6.7 Handling mobility in cellular ll l networks t k o 6.8 Mobility and higherlayer y protocols p

o has many features we’ve seen: o home agents, foreign agents, foreign foreign-agent agent registration, care-of-addresses, encapsulation (packet-within-a-packet) o three h components to standard: d d o indirect routing of datagrams o agent t discovery di o registration with home agent

6.9 Summary 6: Wireless and Mobile Networks

6-64

6-65

6: Wireless and Mobile Networks

6-66

Mobile Mob le IP: IP Agent discovery d scovery

Mobile IP: indirect routing g foreign-agent-to-mobile packet packet sent by home agent to foreign agent: a packet within a packet d t 79.129.13.2 dest: 79 129 13 2

dest: 128.119.40.186

o Agent advertisement: foreign/home agents advertise service i b by b broadcasting d ti ICMP messages (typefield ( f ld = 9) Route advertisement

d t 128.119.40.186 dest: 128 119 40 186

0 t type =9

R bit: registration required

Care-of address: 79.129.13.2

dest: 128.119.40.186

packet sent by correspondent d t 6: Wireless and Mobile Networks

6-67

Mobile Mob le IP: IP registration reg strat on example home agent HA: 128.119.40.7

foreign agent COA: 79.129.13.2

ICMP agent adv. adv ….

COA: 79.129.13.2 HA: 128.119.40.7 MA: 128.119.40.186 Lifetime: 9999 identification: 714 encapsulation format ….

standard ICMP fields

length

registration lifetime

sequence # RBHFMGV bits

reserved

0 or more care-ofaddresses

mobility agent advertisement extension

6: Wireless and Mobile Networks

6-68

Components of cellular network architecture

visited network: 79.129.13/24

COA: 79.129.13.2

registration req.

checksum h k

router address

type = 16

B – Foreign Agent busy M – Min. Encapsulation p G – GRE Encapsulation V– Van Jacobson

24

code = 0

H,F bits: home and/or foreign agent Permanent address: 128.119.40.186

16

8

Mobile agent MA: 128.119.40.186

recall:

correspondent wired public telephone network

registration req.

COA: 79.129.13.2 HA: 128.119.40.7 MA: 128.119.40.186 Lifetime: 9999 identification:714 ….

MSC

MSC MSC MSC

MSC

registration ist ti reply l time

HA: 128.119.40.7 MA: 128.119.40.186 Lifetime: 4999 Identification: 714 encapsulation l ti fformatt ….

registration reply HA: 128.119.40.7 MA: 128.119.40.186 Lifetime: 4999 Identification: 714 ….

6: Wireless and Mobile Networks

different cellular networks, operated db by different diff providers id 6-69

6: Wireless and Mobile Networks

6-70

GSM: indirect routing g to mobile

Handling g mobility y in cellular networks o

Home network: network of cellular p provider you y

home network

HLR

2

subscribe to (e.g., Sprint PCS, Verizon) o Home Location Register (HLR): database in home network containing permanent cell phone #, profile information (services, preferences, billing), information about current location (could be in another network) o Visited network: network in which mobile currently resides o Visitor Vi it L Location ti R Register i t (VLR) (VLR): database d t b with ith entry for each user currently in network o could be home network

home MSC consults HLR, gets roaming number of mobile in visited network

1 VLR

3 Mobile Switching Center

4 mobile user

new base station (without interruption) o reasons for handoff:

Switching Center old routing old BSS

o

new routing

o

new BSS

o

stronger signal to/from new BSS (continuing connectivity, less battery drain) l db load balance: l free f up channel h l in current BSS GSM doesn’t mandate why to perform handoff (policy), (policy) only how (mechanism)

o handoff initiated by old BSS

6: Wireless and Mobile Networks

6-72

GSM: handoff with common MSC GSM

o Handoff goal: route call via

VLR Mobile

MSC in visited network completes call through base station to mobile 6: Wireless and Mobile Networks

6-71

GSM: handoff with common MSC GSM

Public switched telephone network

call routed to home network

home MSC sets up 2nd leg of call to MSC in visited network visited network

6: Wireless and Mobile Networks

correspondent p

home Mobile Switching Center

6-73

VLR Mobile Switching Center 2

4

1 8 old BSS

5

7 3 6

new BSS

1. old BSS informs MSC of impending handoff, a do , p provides o des list st o of 1+ new e BSSs SSs 2. MSC sets up path (allocates resources) to new BSS 3 new BSS allocates radio channel for 3. use by mobile 4. new BSS signals MSC, old BSS: ready 5 old BSS tells mobile: perform handoff to 5. new BSS 6. mobile, new BSS signal to activate new channel 7. mobile signals via new BSS to MSC: handoff complete. MSC reroutes call 8 MSC-old-BSS MSC ld BSS resources released l d 6: Wireless and Mobile Networks

6-74

GSM: handoff between MSCs GSM o home network correspondent

Home MSC

GSM: handoff between MSCs GSM

anchor MSC: ffirst MSC visited during cal o

home network

call remains routed through anchor MSC

o new MSCs add on to end

anchor MSC

PSTN

MSC

MSC

MSC

(a) before handoff

of MSC chain as mobile moves to new M MSC C o IS-41 allows optional path minimization step to shorten multi-MSC chain 6: Wireless and Mobile Networks

Comment on GSM element

anchor MSC

anchor MSC: ffirst MSC visited during cal o

call remains routed through anchor MSC

o new MSCs add on to end PSTN

MSC

MSC

(b) after handoff

of MSC chain as mobile moves to new M MSC C o IS-41 allows optional path minimization step to shorten multi-MSC chain 6: Wireless and Mobile Networks

6-75

6-76

Wireless,, mobility: y impact p on higher g layer y protocols p

Mobile IP element

Home system

Network to which mobile user’s permanent phone h number b b belongs l

Home network t k

Gateway Mobile Switching Center, or “home MSC”. Home Location Register (HLR)

Home MSC: point of contact to obtain routable address of mobile user. HLR: database in home system y containing g p permanent p phone number, profile information, current location of mobile user, subscription information

Home agent

Visited System

Network other than home system where mobile user is currently residing

Visited network

Visited Mobile services Switching Center.

Visitor Location Record (VLR)

Visited MSC: responsible for setting up calls to/from mobile nodes in cells associated with MSC. VLR: temporary database entry in visited system, containing subscription information for each visiting mobile user

Foreign agent

Mobile Station Roaming g Number (MSRN), or “roaming number”

Routable address for telephone call segment between home MSC and visited MSC,, visible to neither the mobile nor the correspondent.

Care-ofaddress

6: Wireless and Mobile Networks

correspondent

Home MSC

MSC

Mobility: Mob l ty GSM versus Mob Mobile le IP GSM element

o

6-77

o logically, impact

should be minimal …

best effort service modell remains unchanged o TCP and UDP can (and do) run over wireless, mobile o … but performance-wise: performance wise: o packet loss/delay due to bit-errors (discarded packets,, delays p y for link-layer y retransmissions), ), and handoff o TCP interprets loss as congestion, will decrease con estion window un-necessarily congestion un necessarily o delay impairments for real-time traffic o limited bandwidth of wireless links o

6: Wireless and Mobile Networks

6-78