Side_1_360

A principle behind the layering is that a layer
entity at a destination sees the same object/mes-
sage as sent by the corresponding layer entity in
the source as illustrated in Figure 7.

An application interacts with a transport proto-
col. The application chooses the format of data
transfer. Two examples are stream (a longer
flow of information) and transaction (an ex-
change of a single information unit). In the
transport layer an association with the transport
layer at the destination is established (frequently
called end-to-end, although when interworking
units are involved the user information could
even be carried further before the final destina-
tion is reached). The transport protocol divides
the data into units, sometimes called segments,
and transfers these units to the IP layer. In the IP
layer, these data units are enveloped by the IP
header information and transferred to the net-
work interface. In a terminal/host that interface
would be interacting with hardware drivers.

Even QoS parameters can be assigned to layers
as illustrated in Figure 8. This implies that dif-
ferent aspects can be discussed on certain layers,
for example allowing for “hiding” characteristics
of lower layers. However, it also raises the need
for finding the mapping between parameter val-
ues on the different layers. When fairly generic
layers are used, such a mapping may not be
straightforward, balancing the requirements of
the upper layers with efficient utilisation of
resources seen by layers below.

3 Optics and IP

Several questioning to what extent the traffic
load growth in the core of IP-based networks is
hindered by the access link capacity (e.g. dial-
up, ISDN, GSM). Introducing access links with
higher capacity, the traffic loads in the core net-
works may grow even more drastically. This is

one argument for investigating use of optics in

closer connection with IP (although the general

traffic growth and price trends for optics also

advocate this).

One of the means to step up the traffic handling

capability of the IP network is to develop routers

with higher throughput. Some means undertaken

are:

• Separate forwarding and route determination
  and make the routing software leaner;


• Introduce interfaces with higher transfer rates,
  increased switching speed;


• Introduce hardware adapted solutions (e.g.
  through application-specific integrated cir-
  cuits, ASICs).

Making leaner software solutions may in some

respects be contrasting the functionality for traf-

fic handling according to the TE mechanisms.

Reducing the number of layers is one step to

reduce the overhead. Hence, IP “directly” over

optics has become a theme gaining more interest.

Figure 8 Layers for TIPHON,

a telephony service, from

[TS329-3]

Figure 7 Hierarchy of

functionality/protocols

e.g. A socket

A port identity

A IP address

Application

Transport

IP

Network

Interface

IP

routing/forwarding

Network Interface

Application

Transport

IP

Network

Interface

e.g. B socket

B port identity

B IP address

Host A Host B

User data Transport layer header IP packet header Link level header

TIPHON voice QoS class user

Jitter, buffer delay, overall one-way application

delay, frame loss, etc.

Packet loss, mean delay, transport

delay variation