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Common Protocols

An Engineering Approach to Computer Networking An Engineering Approach to Computer Networking

The grand finale nn

Previous chapters presented principles, but not protocol detailsPrevious chapters presented principles, but not protocol details

u u

these change with time these change with time

u u

real protocols draw many things together real protocols draw many things together

nn

Overview of real protocolsOverview of real protocols

uu

standards documents are the final resort standards documents are the final resort

n n

Three sets of protocolsThree sets of protocols

u u

telephone telephone

uu

Internet Internet

uu

ATM

ATM

Traditional digital transmission nn

Long distance trunks carry multiplexed callsLong distance trunks carry multiplexed calls

n n

Standard multiplexing levelsStandard multiplexing levels

n n

Digital transmission hierarchyDigital transmission

U S

a n d

J a p a n

M

u l t i p l e x i n g

l e v e l

N a m e

c a l l s

R a t e( M

b p s )

1

D S 1

2 4

1. 5 4 4

2

D S 2

9 6

6. 3 1 2

3

D S 3

6 7 2

4 4. 7 3 6

4

D S 4

4 0 3 2

2 7 4. 1 7 6

Plesiochronous hierarchy nn

PlesiochronousPlesiochronous = nearly synchronous

= nearly synchronous

n n

Tight control on deviation from synchronyTight control on deviation from synchrony

n n

What if stream runs a little faster or slower?What if stream runs a little faster or slower?

nn

NeedNeed

justification justification

Problems with plesiochrony nn

Incompatible hierarchies around the worldIncompatible hierarchies around the world

n n

Data is spread out! Hard to extract a single callData is spread out! Hard to extract a single call

n n

Cannot switch bundles of callsCannot switch bundles of calls

Synchronous Digital Hierarchy nn

All levels are synchronousAll levels are synchronous

n n

Justification uses pointersJustification uses pointers

Data Rate (Mbps)

US Name

OC-

OC-

OC-

OC-

OC-

OC-

OC-

OC-

OC-

SDH nn

9 rows, 90 columns9 rows, 90 columns

n n

Each payload container (SPE) served in 125 microsecondsEach payload container (SPE) served in 125 microseconds

n n

One byte = 1 callOne byte = 1 call

nn

All overhead is in the headersAll overhead is in the headers

nn

Pointers for justificationPointers for justification

u u

if sending too fast, use a byte in the overhead, increasing if sending too fast, use a byte in the overhead, increasing

sending rate sending rate

u u

if sending too slow, skip a byte and move the pointer if sending too slow, skip a byte and move the pointer

uu

can always locate a payload envelope, and thus a call within can always locate a payload envelope, and thus a call within

it => cheaper add drop it => cheaper add drop mux

mux

SDH justification

SS7 example nn

Call forwardingCall forwarding

n n

To registerTo register

u u

call special number call special number

uu

connects to ASE connects to ASE

uu

authenticates user, stores forwarding number in database authenticates user, stores forwarding number in database

n n

On call arrivalOn call arrival

u u

call setup protocol checks database for forwarding number call setup protocol checks database for forwarding number

uu

if number present, reroutes call if number present, reroutes call

nn

SS7 provides all the services necessary for communication andSS7 provides all the services necessary for communication andcoordination between registry ASE, database, and call setupcoordination between registry ASE, database, and call setupentityentity

MTP Header

IP nn

UnreliableUnreliable

n n

Best effortBest effort

n n

End-to-endEnd-to-end

nn

IP on everything- interconnect the worldIP on everything- interconnect the world

IP

IP fields nn

TTLTTL

u u

decremented decremented on each hop

on each hop

u u

decremented decremented every 500 ms at

every 500 ms at endpt

endpt

uu

terminates routing loops terminates routing loops

nn

TracerouteTraceroute

u u

if router decrements to 0, send ICMP error packet if router decrements to 0, send ICMP error packet

u u

source sends packets with increasing TTL and waits for source sends packets with increasing TTL and waits for

errors errors

nn

OptionsOptions

uu

record route record route

u u

timestamp timestamp

u u

loose source routing loose source routing

ICMP nn

Destination unreachableDestination unreachable

n n

Source quenchSource quench

n n

RedirectRedirect

nn

Router advertisementRouter advertisement

nn

Time exceeded (TTL)Time exceeded (TTL)

n n

Fragmentation needed, but Dont fragFragmentation needed, but

Dont frag flag set

flag set